Battery charging circuit

ABSTRACT

A battery charger for recharging a rechargeable battery cell wherein an indication is given as to whether charging current is being drawn. In the charging circuit a capacitor and a rectifying arrangement are connected in series across an ac source and a neon tube and capacitor are connected across the capacitor. With this arrangement the neon tube is illuminated when a charging current is drawn and is not illuminated at other times.

United States Patent [191 Dobie July 17, 1973 [54] BATTERY CHARGINGCIRCUIT 3,539,898 10/1970 Tolmie 320/2 [75] Inventor: Alexander BarbourDoble,

I Newcastle upon Tyne, England Primary Emmm" l D Miller [73] Assignee:Roneon Corporation, w db id Assistant Examiner-Robert J. Hickey NJ.Attorney-Lewis H. Eslinger [22] Filed: Sept. 14, 1972 [21] App]. No.:289,181

4 [57] ABSTRACT [30] Fwd! Application Pmrity A battery charger forrecharging a rechargeable battery Sept. 24, 1971 Great Britain 44,740/71cell wherein an indication is given as to whether charging current isbeing drawn. In the charging circuit a ca- [52] US. Cl. 320/48, 320/2pacitor and a rectifying arrangement are connected in [51 1 Int. Cl."01m 45/06 series aeross an ac source and a neon tube and capaci- Fieldtor are connected across the capacitor. With this ar- 32 2 rangement theneon tube is illuminated when a charging current is drawn and is notilluminated at other [56] References Cited times.

UNITED STATES PATENTS v I I 2,898,5 39 8/ 195 9 Loz'eau 320/48 8 Claims,4 Drawing Figures BATTERY CHARGING CIRCUIT The present invention relatesto a battery charger and more particularly to a battery charging circuitfor charging one or more rechargeable cells from a main AC supply.Typical application for the invention is found in charging circuits forrechargeable electric shavers, tooth brushes and the like.

An object of the present invention is to provide a battery charger inwhich an indication is given according to whether or not chargingcurrent is being drawn.

It is a further object of the present invention to provide a batterycharging circuit which utilizes a neon tube to provide an indication asto whether or not a charging current is being drawn.

According to one embodiment of the present invention there is provided abattery charging circuit comprising terminals for an AC main supply; acapacitor and a rectifying arrangement connected in series across the ACmain supply terminals; DC output terminals connected to the rectifyingarrangement for supplying a battery to be charged; and, connected acrossthe capacitor, a series combination, of a second capacitor and neontube. The battery charging circuit of the present invention is of a kindin which the charging current is limited by a capacitor. Preferably aresistor is connected across the capacitor to discharge the capacitorwhen the circuit is switched off. 7

With the arrangement described above the passage of charging currentbetween the DC output terminals requires an alternating current to passthrough the first mentioned capacitor. When no charging current is beingdrawn from the DC output terminals then the current through the firstmentioned capacitor is negligible. Depending on the particular rectifierarrangement chosen, the corresponding voltage across the first mentionedcapacitor when no charging current is being drawn is either negligibleor is a direct voltage. The second capacitor in series with the neontube serves to limit the neon tube current when the tube strikes and mayalso serve to constitute a voltage blocking device which prevents astriking voltage appearing across the neon tube when the voltage acrossthe first capacitor is a direct voltage.

Thus, it will be seen that the* above described arrangement can ensurethat the neon tube is illuminated when a charging current is drawn fromthe DC output terminals and is not illuminated at other times.

The rectifier arrangement may be a half-wave rectifier or a full-waverectifier. The preferred arrangement for a half-wave rectifier is to usetwo diodes, a first in series with the DC output terminals and a secondacross the series combination of the first diode and the DC outputterminals. With this arrangement a direct voltage is generated acrossthe first mentioned capacitor when no charging current is being drawn.This direct voltage does not cause the neon tube to strike but it may beused in a modified form of the circuit to cause intermittent firing ofthe tube, thus giving a second kind of indicatiomA direct voltage forthis purpose may alternatively be derived from a full-wave bridgerectifier by providing a leakage resistor across one of the diodesthereof. 7

In accordance with the modification mentioned above, a third capacitoris provided in series with a charging resistor across the firstmentioned capacitor,

and thus across the series combination of the second capacitor and theneon tube. The junction of the third capacitor and the charging resistoris joined to the junction of the second capacitor and the neon tube. Theneon tube thereby constitutes part of a relaxation oscillator which, ifa direct voltage is maintained acrossthe first mentioned capacitor,fires the tube intermittently. The firing rate of the tube may beadjusted by adjustment of the component values of the relaxationoscillator circuit.

The invention will be further described with reference to theaccompanying drawings, of which:

FIG. 1 is a circuit diagram of a battery charging circuit in accordancewith one embodiment of the invention;

FIG. 2 is a circuit diagram of a battery charging circuit in accordancewith another embodiment of the invention;

FIG. 3 is a circuit diagram of a battery charging circuit in accordancewith the invention similar to that of FIG. 1 but with a full-waverectifier; and

FIG. 4 is a circuit diagram of a battery charging circuit in accordancewith another embodiment of the invention having a full-wave rectifier.

Referring to FIG. 1 the charging circuit 10 of the present inventioncomprises terminals 12 and 14 across an AC main supply 16 which maytypically be l20 volts at 60 Hz. The battery or cell to be charged isconnected between output terminals 18 and 20 which are connected via ahalf-wave rectifying arrangement 22 having diodes 24 and 26, and acurrent limiting capacitor 28 to the supply terminals 12 and 14. A high'value discharge resistor 30 is connected across capacitor 28 todischarge the capacitor when the circuit is switched off. Also connectedacross capacitor 28 is a series combination of a second capacitor 32 anda discharge illumination tube such as a neon tube 34.

The circuit of FIG. 1 operates in the following manner. If a battery orrechargeable cell is connected between terminals 18 and 20, chargingcurrent is supplied thereto during positive half cycles of the main ACsupply through capacitor 28 and diode 24. Capacitor 28 presents a highimpedance to the supply frequency current and limits the chargingcurrent supplied to the battery or cell to the appropriate value. Duringnegative half cycles the diode 26 conducts and capacitor 28 is chargedin the reverse direction. Therefore, with a bat tery connected betweenterminals 18 and 20, the current through capacitor 28 alternates and thevoltage across the capacitor is an alternating voltage. Because of this,an alternating current is passed through the series combination ofcapacitor 32 and the tube 34 and the tube strikes, thereby beingilluminated. The tube 34 is visible to the user and thus when it isilluminated gives an indication that the battery is being charged.

When the battery draws no charging cur rnt because it is absent there isno conduction through capacitor 28 during the positive half cycles andthe effect of diode 26 is therefore to charge the capacitor 28 with aunidirectional voltage. The minor ripple fluctuations of thisunidirectional voltage are insufficient to cause adequate current topass through capacitor 28 to illuminate the tube 34. Therefore, when nocharging current is being drawn the tube is not illuminated.

It will beappreciated that the reason for no charging current beingdrawn may be that the main supply is switched off or not connectedrather than because the battery is not connected. It is possible toderive from tube 34 an indication which differentiates between these twoconditions. This is achieved by an alternate embodiment as shown in FIG.2 of the drawings. The circuit a of FIG. 2 is similar to that of FIG. 1,with like elements shown with the same numeral designation, except thatacross the series combination of capacitor 32 and tube 34 there isconnected a series combination of a resistor 36 and a third capacitor38. The junction 40 of resistor 36 and capacitor 38 is connected to thejuncture 42 of capacitor 32 and tube 34. This arrangement constitutes arelaxation oscillator which, when there is a unidirectional voltageestablished across capacitor 28, causes the tube 34 to flashperiodically. It will be seen that this condition exists if there is nobattery connected between terminals 18 and but if the main supply 16 isconnected in the circuit. Thus, with the FIG. 2 arrangement there arethree charging indications from the same lamp, namely:

a. a continuously illuminated tube 34 showing that the battery is takingcharge;

b. a flashing tube 34 showing that no charging current is being drawnbut that the main supply is connected in the circuit; and

c. the tube 34 is off showing that the main supply is not connected inthe circuit.

FIG. 3 shows an alternate circuit arrangement 10b similar to FIG. 1 butin which there is a full-wave rectifier arrangement 44 in place of. thehalf-wave rectifier arrangement 22 of FIG. 1. With the bridge full-waverectifier arrangement 44 of FIG. 3 no unidirectional voltage isestablished across capacitor 28 when the battery to be recharged isabsent. However, there are two indications given, as with the FIG. 1arrangement, namely when the tube 34 is illuminated it shows thatcharging current is being drawn and when the tube 34 is not illuminatedit shows that no charging current is being drawn.

FIG. 4 shows an alternate circuit arrangement 10c of the circuit of FIG.3 which allows the above described winking indication to be given with afull-wave rectifier arrangement. In FIG. 4 a leakage resistor 46 isprovided across one of the diodes 48 of the bridge rectifier. Thisallows a unidirectional voltage to be established across capacitor 28when the battery is absent. Thus, the provision of the additionalcapacitor 38 and resistor 36 as in the FIG. 2 circuit arrangement allowsthe circuit to cause tube 34 to give a winking indication if the batteryis absent.

It is thus seen that the present invention provides a battery chargingcircuit in which a visible indication as to whether charging current isbeing drawn is given. In an alternate embodiment of the invention anindication is also given as to whether the AC power supply is connectedinto the circuit.

What is claimed is:

l. A battery charging circuit for charging a rechargeable battery cellcomprising:

terminals for connection to an AC power supply,

a first capacitor and a rectifying arrangement connected in seriesacross said AC power supply terminals,

DC output terminals connected across said rectifying arrangement forsupplying direct current to a battery cell to be charged, and

a series combination of a second capacitor and a discharge illuminatingtube connected across said first capacitor whereby said rectifyingarrangement impresses an alternating current across said secondcapacitor and said illumination tube'when charging current to saidbattery cell is drawn thereby to illuminate said tube to provide avisible indication that charging of said cell is occurring.

2. A circuit as defined in claim 1 wherein said rectifier arrangementcomprises a half-wave rectifier including two diodes, a first diodebeing connected in series with said DC output terminals and the secondof said diodes connected across the series combination of the firstdiode and said DC output terminals.

3. A circuit as defined in claim 2 wherein a series combination of aresistor and a third capacitor are connected across the seriescombination of said second capacitor and said discharge illuminationtube with the junction of said third capacitor and said resistorconnected to the junction of said second capacitor and said tube toprovide a relaxation oscillator arrangement which intermittentlyilluminates said tube when no charging current is drawn but when saidcircuit is con nected to said AC supply.

4. A battery charging circuit as defined in claim 1 including a highvalue discharge resistor connected across said first capacitor todischarge said first capacitor when said circuit is switched off.

5. A circuit as defined in claim 1 wherein said rectifier arrangementcomprises a full-wave rectifier including four diodes arranged as abridge full-wave rectifier connected across said DC output terminals.

6. A circuit as defined in claim 5 wherein a series combination of aresistor and athird capacitor are connected across the seriescombination of said second capacitor and said discharge illuminationtube with the junction of said third capacitor and said resistorconnected to the junction of said second capacitor andsaid tube toprovide a relaxation oscillator arrangementand a second resistorconnected across one of the diodes of said full-wave rectifier bridge toprovide a leakage resistor whereby said illumination tube intermittentlyilluminates when no charging current is drawn but when said circuit isconnected to said AC supply.

7. A charging circuit as defined in claim 5 including a high valuedischarge resistor connected across said first capacitor to dischargesaid first capacitor when said circuit is switched off.

8. A charging circuit as defined in claim 1 wherein said dischargeillumination tube is a neon tube.

l I It!

1. A battery charging circuit for charging a rechargeable battery cellcomprising: terminals for connection to an AC power supply, a firstcapacitor and a rectifying arrangement connected in series across saidAC power supply terminals, DC output terminals connected across saidrectifying arrangement for supplying direct current to a battery cell tobe charged, and a series combination of a second capacitor and adischarge illuminating tube connected across said first capacitorwhereby said rectifying arrangement impresses an alternating currentacross said second capacitor and said illumination tube when chargingcurrent to said battery cell is drawn thereby to illuminate said tube toprovide a visible indication that charging of said cell is occurring. 2.A circuit as defined in claim 1 wherein said rectifier arrangementcomprises a half-wave rectifier including two diodes, a first diodebeing connected in series with said DC output terminals and the secondof said diodes connected across the series combination of the firstdiode and said DC output terminals.
 3. A circuit as defined in claim 2wherein a series combination of a resistor and a third capacitor areconnected across the series combination of said second capacitor andsaid discharge illumination tube with the junction of said thirdcapacitor and said resistor connected to the junction of said secondcaPacitor and said tube to provide a relaxation oscillator arrangementwhich intermittently illuminates said tube when no charging current isdrawn but when said circuit is connected to said AC supply.
 4. A batterycharging circuit as defined in claim 1 including a high value dischargeresistor connected across said first capacitor to discharge said firstcapacitor when said circuit is switched off.
 5. A circuit as defined inclaim 1 wherein said rectifier arrangement comprises a full-waverectifier including four diodes arranged as a bridge full-wave rectifierconnected across said DC output terminals.
 6. A circuit as defined inclaim 5 wherein a series combination of a resistor and a third capacitorare connected across the series combination of said second capacitor andsaid discharge illumination tube with the junction of said thirdcapacitor and said resistor connected to the junction of said secondcapacitor and said tube to provide a relaxation oscillator arrangementand a second resistor connected across one of the diodes of saidfull-wave rectifier bridge to provide a leakage resistor whereby saidillumination tube intermittently illuminates when no charging current isdrawn but when said circuit is connected to said AC supply.
 7. Acharging circuit as defined in claim 5 including a high value dischargeresistor connected across said first capacitor to discharge said firstcapacitor when said circuit is switched off.
 8. A charging circuit asdefined in claim 1 wherein said discharge illumination tube is a neontube.